1. The Field of the Invention
This invention relates to a warming device for shoes and boots, and in particular to a simple device for generating heat within a shoe or boot.
2. Brief Statement of the Prior Art
U.S. Pat. No. 3,534,391 discloses an electrical generator which is mounted on the outside of a ski boot which is driven from a tether that is connected between the generator and a ski. The generated current is passed through heating elements located in the ski boot. The external mounting and tether render this device quite cumbersome and difficult to use.
French Patent Nos. 701,420 and 2,365,973 and U.S. Pat. No. 3,977,093 disclose shoes with batteries mounted in the heels, and with electric resistance heaters in the soles of the shoes. Batteries require frequent replacement, and are particularly inefficient in a cold environment.
U.S. Pat. No. 1,506,282 discloses an electric generator mounted in an telescoping heel of a shoe which generates electricity for an electric lamp, heating coil, wireless outfit or a therapeutic appliance. A telescoping heel of this design would be very difficult to seal against water and mud, and the patented device would most likely be limited to indoor applications.
U.S. Pat. Nos. 2,442,026 and 1,272,931 disclose air pumps which are located in the heels of shoes and operated during walking. In the first mentioned patent, alcohol vapors are mixed with the air stream and passed over a catalyst to generate heat. This system is cumbersome and difficult to use, and it requires replenishing the alcohol. Also, the heater elements are open in the shoe for air and gas circulation. In U.S. Pat. No. 1,272,931, the air is forced through constricted passageways to generate heat by compression. The heated air is openly discharged into the shoe, as there is no provision for a closed loop air path.
U.S. Pat. No. 382,681 discloses an armature which is mounted in a heel and manually rotated to generate heat by friction, which is dissipated in the shoe by metal conductors. U.S. Pat. No. 3,493,986 discloses an inner sole for a shoe which is formed of piezoelectric or magnetostrictive material which generate heat while the user walks.
U.S. Pat. No. 2,475,092 discloses a bouncing skate having spring coils on the bottom of its sole. German Patent Nos. 180866 and 620,963, and U.K. Patent No. 443,571 disclose springs mounted within a shoe for orthopedic purposes. None of these patents disclose shoe heaters.
U.S. Pat. No. 4,507,877 discloses a heater for a ski boot which is mounted on the inner shoe of the boot and which includes rechargeable storage batteries, control switch and electrical heating coil. Products of this design have been marketed with chargeable and with nonrechargeable batteries. These units do not provide any sustained heating, but are useful only to provide monetary heating because of the limited storage capacity of small batteries and the low efficiencies which they experience at sub-freezing temperatures.
All of the aforementioned attempts have failed to provide a practical self sustaining heater within a shoe which harnesses the movement between the wearer's heel and the heel of the shoe to generate heat. This relative movement can be sufficient, particularly when the wearer's weight is applied, to generate the necessary heat, provided a practical heat generator can be installed within the narrow confines of the shoe and heel, without significantly affecting its external appearance and comfort.
Air bags have been positioned in ski boots, over the instep and forefoot, and have been provided with inflation pumps to provide a variable control on the snugness of fit of the boots. U.S. Pat. No. 4,420,893 discloses an air pump which is operated by the flexing of the ankle during normal skiing actions to circulate fresh air through a ski boot. While this may be useful to reduce the humidity within a boot, it would not be suitable in very cold weather.